Linear motion guide device

ABSTRACT

A linear motion guide device has a high rigidity, a good linear motion guiding accuracy, and as little rattling as possible. The linear motion guide device prevents sand, water or other contaminants from entering its actuator main body, and features low maintenance requirement. A linear motion member of the linear motion guide device includes is constituted by a plurality of axially divided segments. Each of these segments supports a plurality of guided members which make contact with two, mutually paired, guide surfaces of a housing. A preload can be applied between the guide surfaces and the guided member. The housing has a sealed structure, with a pressure inside the housing higher than an external pressure, for preventing external sand and water from entering the housing.

TECHNICAL FIELD

The present invention relates to linear motion guide devices used inlinear motion guides for machine tools, measuring apparatuses, transportapparatuses, etc., and more specifically to a linear motion guide devicewhich is suitable to guiding a linear motion member of a solar orbitaltracking mechanism in a solar photovoltaic/thermal power generationapparatuses.

BACKGROUND ART

A linear motion guide used in a positioning section of, e.g., a machinetool, may include a component as shown in FIG. 16 A and FIG. 16 B, whichis called linear rail guide (also called linear motion rolling bearing).The component is an assembly of a linear rail 30 and a sliding unit 31which slides along the linear rail 30. The linear rail guide has a largevariety in its size and shape, etc., and a wide range of the product isavailable from a number of manufacturers according to specificapplication requirements such as expected load, mounting attitude, etc.

Linear rail guides which are currently used widely can be divided intotwo types: One is called circulation type, in which rolling elements(not illustrated) such as balls and rollers in the linear rail guidecirculate inside the sliding unit 31. The other type is called finitestroke type, in which rolling elements called cross roller guides staycaptured by a retainer. For increased durability, both types make use ofhardened steel such as a bearing steel for their linear rail 30 whichprovides a guide surface and for the rolling elements. As understoodfrom the example in FIG. 16 A, FIG. 16 B, a ball screw mechanism and alinear rail guide are combined in parallel with each other, so that theball screw mechanism will not come under a direct radial or moment load.This arrangement provides highly durable and accurate linear motionguides.

There are linear motion guides which do not make use of the linear guiderail: Patent Literatures 1 through 4 disclose techniques forimplementing such linear motion guides by using vertical grooves andvertical guide surfaces formed on, e.g., an inner surface of a housing,etc., and a cam follower or other bearings which move along thesevertical grooves and vertical guide surfaces. Also, Patent Literature 5discloses a technique of implementing a linear motion guide by arranginga plurality of bearings in a circumferential direction of a housing, sothat outer ring surfaces of these bearings make contact with a linearmotion member disposed at a center.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2007-216280

Patent Literature 2: JP-A-H2-186157

Patent Literature 3: JP-A-2010-179323

Patent Literature 4: JP-A-2007-333046

Patent Literature 5: JP-A-2001-221229

FIG. 17 shows a cylinder linear motion actuator 7 driven by a motor 6.Such an actuator is being introduced as a replacement for air cylindersin production/transportation facilities for energy saving purposes. Thiscylinder type linear motion actuator makes use of a linear motion guidemechanism as a critical component, and by far this linear motion guidemechanism determines an outlook, cost and performance of the cylinderlinear motion actuator.

Although the linear motion guide mechanism implemented by a linear railguide offers high rigidity and superb linearity, it requires, as shownin FIG. 16 A, FIG. 16 B, a large number of fasteners 32 such as bolts inorder to fix a straight rail 30, and this poses a hurdle in space savingand cost reduction.

The linear motion guide mechanisms which do not employ linear railguides also have problems. Specifically, the disclosures in PatentLiteratures 1 through 4 may be divided into two categories: firstcategory (Patent Literatures 1, 2) with a primary object of preventingrotation of a linear movement member used in a mechanism for convertingrotating movement into linear movement, and a second category (PatentLiteratures 3, 4) with a primary object of making the mechanism capableof bearing an amount of load. However, even the latter ones are stilllimited in the direction of the load due to the number and locations ofbearings. In particular, they are not applicable to loads exerted fromoblique directions.

Patent Literature 5 discloses a technique for bearing a load fromvarious directions. However, complicated procedures have to be followedto fix bearings and to adjust pressures at which the bearings arepressed onto a linear motion member.

When a linear motion guide device is utilized in solar orbital trackingcomponents in solar photovoltaic/thermal power generation apparatuses,low maintenance features are essential. Furthermore, the device must behighly capable of preventing sand and water from entering actuator mainbodies because the power generation apparatuses are usually installed ina huge number and in extreme environmental conditions such as in desertareas.

It is therefore an object of the present invention to provide a linearmotion guide device which has high rigidity and high linear motionguiding accuracy with as little rattling as possible.

Another object of the present invention is to provide a linear motionguide device which requires as little maintenance as possible bypreventing sand, water and others from entering an actuator main body.

SOLUTION TO PROBLEM

A linear motion guide device according to the present inventionincludes: a housing; a threaded shaft supported by the housing rotatablyabout a center axis but axially immovably; and a linear motion memberincluding a nut threaded around the threaded shaft, for movement axiallyof the threaded shaft by rotation of the threaded shaft. In this device,the housing includes a plurality of guide surfaces along the axialdirection of the threaded shaft; the guide surfaces are provided bypairs of two surfaces; and the two guide surfaces in each pair are notparallel with each other but face away from each other. The linearmotion member includes a plurality of segments arranged axially of themember and connected to each other; and each segment supports aplurality of guided members for contact with respective guide surfaces.

The segments are connected to each other so as to give a preload betweenthe guide surfaces and the guided members.

By making the pressure inside the housing higher than the externalpressure, it is possible to prevent external sand and water fromentering the housing.

In order to reduce pressure difference between a compressing side and anexpanding side caused by a reciprocating movement of the linear motionmember, it is preferable that the housing has a vent filter.

A buffer member may be provided between the housing and the linearmotion member.

Alternatively, a spring mechanism which maintains a constant pressuremay be provided between the housing and the linear motion member.

Advantageous Effects of Invention

A linear motion guide device according to the present invention includesa linear motion member which is constituted by an axially dividedplurality of segments, and each of these segments supports a pluralityof guided members making contact with two paired guide surfaces. Sincethe arrangement makes it possible to give a preload between the guidesurface and the guided member, the device provides increased rigidityand good linear motion guiding accuracy while reducing rattling.

Also, the linear motion guide device according to the present inventionis highly capable of preventing sand and water from entering itsactuator main body, and therefore does not require high maintenance.Hence, the device can be used appropriately as a linear motion memberfor a solar orbital tracking system in solar photovoltaic/thermal powergeneration apparatuses.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a partially broken side view of a linear motion actuatorwhich includes a linear motion guide device according to an embodimentof the present invention.

FIG. 1B is a sectional view taken in lines IB-IB in FIG. 1A.

FIG. 2 is a partially enlarged view of FIG. 1A.

FIG. 3 is a partially enlarged view of FIG. 1B.

FIG. 4 is a sectional view showing a different example of a guidesurface of the linear motion guide device.

FIG. 5 is a sectional view showing still another different example ofthe guide surface.

FIG. 6 is a sectional view showing still another different example ofthe guide surface.

FIG. 7 is a sectional view showing still another different example ofthe guide surface.

FIG. 8 is a sectional view showing a different example of a guidedmember of the linear motion guide device.

FIG. 9 is a sectional view showing still another different example ofthe guided member.

FIG. 10 is a sectional view showing still another different example ofthe guided member.

FIG. 11 is a partially unillustrated, partially broken side view of alinear motion guide device according to a different embodiment of thepresent invention.

FIG. 12 is a sectional view of the embodiment shown in FIG. 11.

FIG. 13 is a sectional view of an embodiment including a housing havingan inner surface formed with five track grooves.

FIG. 14 is a partially broken side view of a linear motion actuatorwhich includes a linear motion guide device according to anotherembodiment of the present invention.

FIG. 15 is a partially broken side view of a linear motion actuatorwhich includes a linear motion guide device according to anotherembodiment of the present invention.

FIG. 16A is a partially broken side view of a conventional linear motionguide device. FIG. 16B is a sectional view taken in lines XVIB-XVIB inFIG. 16A.

FIG. 17 is a partially broken side view of a conventional linear motionactuator.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described with referenceto FIGS. 1A, 1B through FIG. 3.

Referring to FIG. 1A and FIG. 1B, a linear motion guide device 1includes a linear motion member 5 which has a housing 2; a threadedshaft 3 supported by the housing 2 rotatably around the center axis butimmovably along the axis; and a nut 4 threaded around the threaded shaft3. The linear motion guide device 1 constitutes a linear motion actuator7 together with a motor 6 which serves as a driving source.

The housing 2 has a cylindrical linear motion guide section 2 a; athreaded-shaft support section 2 b which is connected to one of twoleft-right ends of the linear motion guide section 2 a; a couplingstorage section 2 c which is connected to an end of the threaded-shaftsupport section 2 b; a shaft support section 2 d which is connected tothe other of the left-right ends of the linear motion guide section 2 a;and a cap section 2 e which is connected to an end of the shaft supportsection 2 d.

The threaded shaft 3 has a ball screw section 3 a for the nut 4 tothread around; a cylindrical surface section 3 b which continues fromthe ball screw section 3 a toward a base end; and a male-thread section3 c. The threaded shaft 3 is supported at the cylindrical surfacesection 3 b rotatably by a multiple-row support bearing 8 which isfitted to an inner circumference of the threaded-shaft support section 2b of the housing 2. The support bearing 8 is provided by, e.g., arolling bearing such as an angular contact ball bearing. The male-threadsection 3 c is threaded with a retaining nut 9, so the threaded shaft 3is axially immovable. The threaded shaft 3 is connected to a rotationshaft 6 a of the motor 6 which is disposed outside of the housing 2, viaa coupling 10 placed inside the coupling storage section 2 c.

The nut 4 is provided, e.g., by a ball nut which includes balls (notillustrated) that make circulating movement along a contact surface withthe ball screw section 3 a of the threaded shaft 3. The ball screwsection 3 a and the nut 4 constitute a ball screw mechanism 11. In theball screw mechanism 11, the linear motion member 5 including the nut 4makes axial movement as the threaded shaft 3 is rotated.

The linear motion member 5 includes the nut 4, a moving bracket 12fitted around an outer circumference of the nut 4, and a shaft 13extending axially of the threaded shaft 3 from the moving bracket 12.The nut 4 and the moving bracket 12 are connected to each other in amutually non-rotatable fashion by means of splines for example, and aremade axially immovable with respect to each other by unillustratedretaining means.

The moving bracket 12 is an assembly of an axially divided plurality ofsegments 12 a, 12 b. The embodiment shown in FIGS. 1A and 1B throughFIG. 3 is an example in which the bracket is divided into two segments.

The segments 12 a, 12 b are connected and fixed to each other by setscrews 27 so that their relative rotation angle around the threadedshaft 3 can be varied.

As shown in FIG. 2, the shaft 13 is cylindrical, and into its hollowspace, a tip portion of the threaded shaft 3 extending out of the nut 4is inserted. The shaft 13 is supported axially slidably along thethreaded shaft 3 by a linear motion sliding bearing 14 which is fittedto an inner circumference of the shaft support section 2 d of thehousing 2. The moving bracket 12 and the shaft 13 maybe integral witheach other or separate from each other.

As shown in FIG. 1B, the linear motion guide section 2 a of the housing2 has a substantially square section when cut perpendicularly to theaxial direction of the threaded shaft 3, and is hollow, having an innersurface formed with a plurality of guide surfaces 15 (15A through 15D)of a consistent width axially of the threaded shaft 3. Each guidesurface 15 is for guiding a guided member 16, which will be describedlater, axially of the threaded shaft 3. In the illustrated example, atotal of four guide surfaces 15, i.e., a pair on the left side andanother pair on the right side, are formed. These guide surfaces 15 aregrouped in two pairs of an upper and a lower surfaces: Namely, the guidesurface 15A and the guide surface 15B make a pair, whereas the guidesurface 15C and the guide surface 15 d make the other pair. In eachpair, the guide surfaces 15 are not in parallel with each other and arefacing away from each other. In other words, in each pair, the guidesurfaces 15 would cross each other if they are extended. In each pair,the guide surfaces 15 are slanted with respect to a flat bottom surfaceF of the housing 2, by an angle of plus 45° and minus 45° respectively(θA, θB, θC and θD=45°).

Each of the segments 12 a, 12 b of the moving bracket 12 in the linearmotion member 5 has a support portion supporting guided members 16 whichmake contact with the guide surfaces 15. Each guided member 16 is formedof a guide bearing which includes a trunnion shaft 17 extending radiallywith respect to the threaded shaft 3 from an outer surface of therespective segments 12 a, 12 b which constitute the moving bracket 12;and a rolling bearing 18 mounted to the trunnion shaft 17 so that thebearing's outer circumferential surface makes rolling contact with theguide surface 15. In each guided member 16, the trunnion shaft 17 hasits center axis P crossing a center axis O of the threaded shaft 3. Inthis embodiment, the rolling bearing 18 is provided by a deep grooveball bearing.

The segments 12 a, 12 b are connected and fixed to each other with setscrews 27 so that their relative rotation angle around the threadedshaft 3 can be varied. Therefore, it is possible to vary a contactpressure between the guided member 16 and the guide surface 15. Thisallows preload adjustment between the guided member 16 and the guidesurface 15.

In the linear motion actuator 7 which makes use of the linear motionguide device 1, the motor 6 drives and rotates the threaded shaft 3,whereby the linear motion member 5 including the nut 4 is moved axiallyof the threaded shaft 3. In this movement, the plurality of guidedmembers 16 on the moving bracket 12 of the linear motion member 5maintain their contact with a corresponding one of the guide surfaces 15formed in the housing 2, thereby accurately guiding the linear motionmember 5 axially with respect to the threaded shaft 3.

Since these guide surfaces 15 are formed in pairs, and since two guidesurfaces 15 in each of the two pairs are not in parallel with each otherand are facing away from each other, a load exerted onto the linearmotion member 5 is spread to all of the guide surfaces 15. Therefore, itis possible to receive loads from various directions and/or a big load.Also, the two guided members 16 which make contact with the respectivepair of guide surfaces 15 (15A and 15B, or 15C and 15D) which face awayfrom each other can be press-fitted onto their respective guide surfaces15 by rotating the segments 12 a, 12 b relatively from each other aroundthe threaded shaft 3 and then fixing to each other by using the setscrews 27. Since this results in a structure in which the guided members16 grasp a portion of the housing 2 which is sandwiched by the two guidesurfaces 15, in a compressing manner, this improves rigidity of thehousing 2. Since the guide surfaces 15 are arranged in such a mannerthat they are in pairs, and are on both sides of the threaded shaft 3 interms of a diametrical direction, it is possible to support the loadexerted onto the linear motion member 5 in a well balanced fashion withthe pairs of guide surfaces 15. Since the guide surfaces 15 are formedon an inner surface of the housing 2 and it is not necessary toseparately provide rails for guiding the guided members 16, it ispossible to make the device compact.

In the present embodiment, the guided member 16 is provided by a guidebearing which includes a trunnion shaft 17 and a rolling bearing 18, andthe rolling bearing 18 has its outer ring 18 a making rolling contactwith the guide surface 15. Therefore, friction resistance between theguide surface 15 and the guided member 16 is small, and it is possibleto move the linear motion member 5 smoothly. Also, the rolling bearing18 is provided by a deep groove ball bearing, which is easy to assemble,widely available and is low cost.

As exemplified in FIG. 4, the guide surface 15 may be a curved surfacewhich has an arc-like convex section in a sectional view which is takenvertically to the center axis O of the threaded shaft 3. In this case,the arrangement prevents the rolling bearing 18 from making contact onan edge of an outer circumferential surface of the outer ring 18 a withrespect to the guide surface 15.

Also, as shown in FIG. 5, an axially extending oil storage groove 20 maybe formed within a width of the guide surface 15 which makes contactwith the rolling bearing 18. In this case, the arrangement prevents lackof lubrication oil on the outer circumferential surface of the outerring 18 a in the rolling bearing 18, leading to improved durability ofthe rolling bearing 18.

As shown in FIG. 6, a platy member 21 which has a higher surfacehardness than the guide surface 15 may be placed between the guidesurface 15 and the rolling bearing 18 for wear resistance. The platymember 21 may be adhesively provided on a surface of the guide surface15 for example. In this case, the arrangement improves durability of theguide surface 15 against wear from rolling contact by the rollingbearing 18.

Instead of using the platy member 21, a surface hardening treatment maybe provided to the guide surface 15. This also improves durability ofthe guide surface 15. Alternatively, the entire housing 2 may be heattreated for increased hardness. This also improves durability of theguide surface 15.

As shown in FIG. 7, the housing 2 may be constituted by a housing mainbody 2A and a guide surface formation member 22 which has a guidesurface 15 and is fixed to the housing main body 2A. The housing mainbody 2A and the guide surface formation member 22 are fixed with boltsor other appropriate methods. In this case, the arrangement makes iteasy to form the guide surface 15.

As shown in FIG. 8, the rolling bearing 18 may be provided by aplurality of angular contact ball bearings which are assembledback-to-back or face-to-face, axially around the trunnion shaft 17.These angular contact ball bearings should desirably be preloaded. Therolling bearings 18 provided by multiple angular contact ball bearingsmake the device capable of receiving not only a load vertical to theguide surface 15 but also a load from a width direction of the guidesurface 15. Also, a preload eliminates a gap between the bearings, andincreases rigidity.

As shown in FIG. 9, instead of a combination of the trunnion shaft 17and the rolling bearing 18, the guide bearing constituting the guidedmember 16 may be formed of a cam follower 24 which includes a shaft 24 aand a roller 24 c attached around an outer circumference of the shaftvia rolling elements 24 b and functioning also as an outer ring. In thecam follower 24, its outer ring, i.e., the roller 24 c, makes widercontact than in the rolling bearings 18 provided by a deep groove ballbearing or an angular contact ball bearing, so it is possible toincrease a load capacity in a single component. If the rolling elements24 b are provided by rollers such as cylindrical rollers, it is possibleto increase the load capability further. Also, since the cam follower 24does not have an inner ring, it can be disposed in a diametrically tightspace.

In cases where the guide bearing is provided by the rolling bearing 18or the cam follower 24 which makes rolling contact with the guidesurface 15, a resin coating with polyurethane for example, may beprovided on an outer circumferential surface of the outer ring 18 a or24 c of the guide bearing. This can improve slidability between theouter ring 18 a or 24 c and the guide surface 15.

As shown in FIG. 10, the guided member 16 may make sliding contact withthe guide surface 15. This guided member 16 includes a support member 25extending radially outward from the moving bracket 12, and a slidingcontact member 26 fixed thereon for making sliding contact with theguide surface 15. The guided member 16 which makes sliding contact withthe guide surface 15 also can guide the linear motion member 5accurately along the axial direction of the threaded shaft 3.

FIG. 11 shows an arrangement where the moving bracket 12 of the linearmotion member 5 is formed of three axially arranged segments 12 a, 12 b,12 c, and each of the three segments 12 a, 12 b, 12 c has three guidedmembers 16 at an interval of 120° in a rotating direction of thethreaded shaft 3.

In the embodiment shown in FIG. 11, three axially extending linear trackgrooves 28 are formed as shown in FIG. 12, in an inner surface of thehousing 2, and mutually opposing walls in each track groove 28 provideguide surfaces 15 for the guided member 16.

FIG. 13 shows an example in which five axially extending linear trackgrooves 28 are formed in an inner surface of the housing 2, and mutuallyopposing walls in each track groove 28 provide guide surfaces 15 for theguided member 16.

When the linear motion guide device 1 is utilized in solar orbitaltracking components in solar photovoltaic/thermal power generationapparatuses, low maintenance features are essential and the device mustbe highly capable of preventing sand and water from entering actuatormain bodies because the generation apparatuses are usually installed ina huge number under extreme environmental conditions such as in desertareas.

For this reason, it is preferable that the housing 2 has a sealedstructure, and the housing 2 has its internal pressure kept higher thanexternal pressure. By making the pressure inside the housing 2 higherthan the external pressure, it becomes possible to prevent external sandand water from entering the housing 2. The pressure inside the housing 2can be made higher than the external pressure by, for example,connecting a pressurizing pump 29 to the housing 2 as shown in FIG. 14.

If sealed structure is used for the housing 2, the reciprocating linearmotion member 5 creates pressure difference within the housing 2, withair compressed on one side while expanded on the other side. In order toreduce the pressure difference, it is preferable to use a vent filter 30in the housing 2 as shown in FIG. 15.

Also, a buffer member may be provided between the housing 2 and thelinear motion member 5.

Alternatively, a spring mechanism which maintains a constant pressuremay be provided between the housing 2 and the linear motion member 5.

REFERENCE SIGNS LIST

-   1 Linear Motion Guide Device-   2 Housing-   2A Housing Main Body-   3 Threaded Shaft-   4 Nut-   5 Linear Motion Member-   6 Motor-   7 Linear Motion Actuator-   12 Moving Bracket-   12 a, 12 b, 12 c Segments-   15, 15A, 15B, 15C, 15D Guide Surface-   16 Guided Member-   17 Trunnion Shaft-   18 Rolling Bearing-   18 a Outer Ring-   20 Oil Storage Groove-   21 Platy Member-   22 Guide Surface Formation Member-   24 Cam Follower-   24 c Roller (Outer Ring)-   26 Sliding Contact Member-   27 Set Screw-   28 Track Groove-   29 Pressurizing Pump-   30 Vent Filter

1. A linear motion guide device comprising: a housing; a threaded shaftsupported by the housing rotatably about a center axis but axiallyimmovably; and a linear motion member including a nut threaded aroundthe threaded shaft, for movement axially of the threaded shaft byrotation of the threaded shaft; the housing including a plurality ofguide surfaces along the axial direction of the threaded shaft; theguide surfaces being provided by pairs of two surfaces; the two guidesurfaces in each pair being not parallel with each other but facing awayfrom each other; the linear motion member including a plurality ofsegments arranged axially of the member and connected to each other;each segment supporting a plurality of guided members for contact withrespective guide surfaces, wherein the plurality of segments areconnected to each other so as to give a preload between the guidesurfaces and the guided members.
 2. The linear motion guide deviceaccording to claim 1, wherein each of the segments includes trunnionshafts each extending radially with respect to the threaded shaft, andeach of the guided members is a guide roller supported by a respectiveone of the trunnion shafts.
 3. The linear motion guide device accordingto claim 1, wherein the guided member is a slidable sliding member. 4.The linear motion guide device according to claim 1, wherein the housingis configured to maintain an internal pressure higher than an externalpressure.
 5. The linear motion guide device according to claim 1,wherein the housing includes a vent filter for reducing a pressuredifference between an air-compression side and an air-expansion sidecaused by a reciprocating movement of the linear motion member withinthe housing.
 6. The linear motion guide device according to claim 1,further comprising a buffer member between the housing and the linearmotion member.
 7. The linear motion guide device according to claim 1,further comprising a spring mechanism placed between the housing and thelinear motion member, the spring mechanism being configured to maintaina consistent air pressure.